Underlayment is a thin layer of high-density protective foam that is installed between the subfloor and hardwood floors to provide a barrier that dampens sound, protects your beautiful hardwoods from mold, mildew and moisture. It is recommended to spend as much as possible on underlayment, as the performance is generally lower than the price of underlayments. There are two main categories of underlying layers: rigid lower layers and soft lower layers. Rigid lower layers are typically wood sheets or cement boards, while soft lower layers are usually loose and soft.
Manufacturers of laminate floors often state that a loose underfloor should not be used with a pre-placed subfloor. If the planks of your laminate floor already have a subfloor pad, do not use any additional underlayment, as doing so will cancel out the Swiss Krono guarantee. In many high-rise buildings, it is a requirement of the BCA (Australian Building Code) that tiles be installed on a lower layer for acoustic purposes.